1. Field of the Invention
This invention relates generally to the field of switch matrices and, more particularly, to radio frequency (RF) switch matrices.
2. Description of the Related Art
In the processes involved in product development, product testing, or research experiments, there is often a need to connect one or more instruments to one or more RF signals. Each of a plurality of independent signals may need to be connected to one or more instruments. Such connections, involving one or more sets with each set including one or more independent instruments and one or more independent signals, may be accomplished using a traditional switch matrix. A switch matrix allows row terminals to connect to column terminals. A full matrix topology has a switch or relay at every row-column crosspoint. FIG. 1 illustrates this topology with one single pole, single throw (SPST) switch at every row-column crosspoint (note: row 0 is connected to column 1 and row 2 is connected to column 3 in FIG. 1). While this topology allows as many simultaneous routes as the smaller of the number of rows or the number of columns, it is expensive to provide a switch or relay for every crosspoint. A column-to-column connection is not possible without simultaneously energizing a row. Similarly, a row-to-row connection is not possible without simultaneously energizing a column.
In addition, as shown in FIG. 2, a full switch matrix is not ideal for carrying high frequency signals, because the unused portion of the connected traces (shown as a dashed line) adds capacitive load and Signal stubs to the transmission lines. This results in reflections that can distort and attenuate the signal. These reflections can vary from one crosspoint position to another due to Signal stubs of varying length. FIG. 3 shows a full blocking matrix that trims any excess stubs from the connected row and column. However, this topology does not allow row-to-row or column-to-column connectivity, nor does it allow a column to connect to more than one row or a row to connect to more than one column.
An alternative to a full matrix is a sparse matrix. This topology allows only a limited number of simultaneous row-to-column connections—often only one connection at a time. Sparse matrices are generally made from two multiplexers with their common ports tied together, as shown in FIG. 4 (note: row 1 is connected to column 3 in FIG. 4). Sparse matrices use fewer relays and are less expensive than full matrices. A typical sparse matrix can make a single, stub-free connection between one column port and one row port.
More complicated signal routing connection pathways would benefit from a switch matrix with more versatile connection options than provided by a traditional switch matrix. It would be advantageous to be able to connect any subset of the switch matrix ports to any other subset of the remaining ports. High frequency signal applications would also benefit from a switch matrix with improved high frequency signal routing and transmission characteristics.